Lubricants are critical in getting electrical switches to meet their life and operating specifications. Choosing the right one requires a full understanding of the switch and its environment. Lubricants improve switch performance in three ways. Primarily, they prevent environmental and galvanic corrosion on switch contacts. Airborne contaminants attack metals, causing oxides to gradually build up in pores until they reach the surface, where they impede current flow. Non-noble contact surfaces and switches made of dissimilar metals are especially susceptible to moisture, oxygen, and aggressive gases. Even noble-metal plating is at risk if it's worn or porous.
Lubricants also minimize wear, especially on sliding electrical contacts which see repetitive cycling or arc damage, two common causes of failures. Though evidence suggests lubricants change or reduce arc patterns, the lubricant's real job on sliding contacts is to separate the surfaces during operation and keep debris out of the contact area. Otherwise, the microscopic wear particles oxidize quickly, turning into insulators. Buildup of this oxide grit also accelerates wear. In general, hydrocarbon lubricants work best at wear prevention because their molecular structure is more rigid than other base oils. Proper lubricants strike a balance between preventing wear and maintaining electrical continuity.
And finally, lubricants reduce the friction between switch components, thus reducing the amount of force needed to activate a switch. Lubricants usually ensure a coefficient of friction of 0.1 or less, which means it takes little force to operate a device with a high preload. This can be important in switches where high normal forces ensure low contact resistance and a stable signal or power path. Lubrication is also mechanically important because it gives the end user smooth, uniform operation.
Damping greases (high-viscosity lubricants) are used to provide drag and give switches a “high-quality” feel. Although silicones historically have been used as damping greases, new high-molecular weight polymers offer a similar feel without fear of silicone migration, which is more than an aesthetic problem. Under arcing, silicone degrades to silicon dioxide (sand), an abrasive and insulating by-product that destroys contacts quickly.
Safety when working around high voltage switches is a major concern. Having to manually apply lubrication to transformers and high voltage electrical switches poses a safety and health risk, but it is necessary to lubricate because high current levels also raise the issue of arcing. Under an arc, temperatures can reach 1,000 C. At that temperature, most metals become molten and most hydrocarbons polymerize, becoming a tacky, viscous, insulating film that is not easily displaced. No material can withstand this abuse, and eventually the switch fails, causing an open circuit. To prevent arcing, choose a lubricant with the longest life under such conditions. In theory, lubricants that vaporize instead of polymerize—such as polyglycols and PFPEs—work better because they leave no insulating residue. However, as a lubricant vaporizes, less remains to lubricate.
The ability to apply a lubricating substance from a safe distance from the apparatus is ideal.
The impact-rupturable pellet containing the lubricating substance as described in this invention are set into projectile motion with the shell substantially intact at a velocity sufficient to create the force permitting rupture of the shell and release of the liquid dye composition therein upon physical impact with the target surface. Typically, the suitable velocity range is from about 200 ft/sec to about 400 ft/sec, preferably within a range from about 300 ft/sec to about 350 ft/sec. Such devices are typically in the form of a gun assembly adapted for use with the pellet. The gun assembly is commonly referred to as a lubricating pellet gun or “marker.” Suitable lubricating pellet guns include commercially available models such as those from Brass Eagle (Bentonville, Ark.). Accordingly in use, the impact-rupturable capsule is removed from a container and loaded into the lubricating pellet gun. The gun is aimed at the intended target and fired, ejecting the impact-rupturable capsule substantially intact at high speed toward the target through the use of pressurized CO.sub.2 or N.sub.2. Upon impact on the target surface, the shell ruptures thereby releasing the liquid contents within onto the surface.